The general aim of this project is to examine adjunct structures to the excitable membranes of nerve and muscle. The influence of these structures on both physiological behavior and on measurements and analysis of excitable membrane properties is sought. Extruded axoplasm from the squid giant axon is examined by gel electrophoresis. Amino acid analyses are carried out on polypeptide chains eluted from various gel bands. Comparison of squid axoplasm proteins and those found in other tissures and species is sought. Electronmicroscopy is used to investigate the anatomical dimensions of the Schwann cell layer external to axon membranes of Loligo and Myxicola. These dimensions are used to predict both physiological behavior and the value of the resistance in series with the excitable membranes. Values of series resistance in these two preparations are measured electrically by means of current clamp and impedance techniques. Electrical measurements are also used to determine the resistivity of axoplasm. Comparisons are made among values obtained by biophysical, biochemical, and anatomical approaches to characterizing these adjunct structures.